<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
    html {
      height: 100%;
    }

    body {
      margin: 0;
      height: 100%;
    }

    .sb {
      width: 400px;
      height: 400px;
      background-color: azure;
    }

    .son {
      width: 50%;
      height: 50%;
      background-color: aqua;
    }

    .son2 {
      width: 50vw;
      height: 50vh;
      background-color: aquamarine;
    }
  </style>
  <title>Document</title>
</head>

<body>

  <div class='sb'>
    <div class='son'><span style="font-size: 10vw;">250</span></div>
    <div class="son2">
      <span style="font-size: 10vw;">250</span>
    </div>

  </div>


  <script>
    const divs = document.querySelectorAll('div');
    divs.forEach((div) => {
      div.addEventListener('mouseenter', function () {
        this.style.backgroundColor = 'yellow';
        // this.style.border = '10px solid #fff';
        // this.style.padding = '30px';
      })
      div.addEventListener('mouseleave', function () {
        this.style.backgroundColor = 'aquamarine';
      })
    })
  </script>
</body>

</html>